Development of an Ionosphere-Plasmasphere-Polar Wind Model and Studies of Storms and Substorms (original) (raw)
Related papers
Empirical modelling of ionospheric storms at midlatitudes
Advances in Space Research, 1998
The reaction of the F-layer to geomagnetic storms is studied between 35' and 55" (dipole latitude) with as indicator the relative deviation of foF2 to its monthly median. A longitude/UT Fourier development yields the longitudinally averaged offset, the diurnal and the semkiiurnal wave. These are evaluated in terms of the total energy input into the aurora1 thermosphere ("Power Index". P) as solutions of a continuity equation written for this ionospheric characteristic. Production, loss and drift terms are introduced in the equation, representing the main physical processes controlling the ionospheric disturbances during storms. The ionospheric characteristic is presented as the sum of the average offset and the slowly rotating standing wave. The expression matches the data satisfactorily for storms in the summer hemisphere, while in winter there is significant discrepancy, possibly as a consequence of interhemispheric influences. 01998 COSPAR.
Journal of Geophysical Research, 1996
Model calculations of the electrodynamics of the high-latitude ionosphere are compared to measurements made by the Viking satellite during July-August 1986. The model calculations are based on the IZMEM procedure, where the electric field and currents in the ionosphere are given as functions of the interplanetary magnetic field. The events chosen correspond to the growth, the expansion, and the recovery phases of substorms. During the growth and expansion phases the correlation between the model results and the satellite data is rather good. During recovery phase the correlation is not as good. The correlation between modeled and observed quantities suggest that during growth and expansion phase the magnetosphere is mainly directly driven by the solar wind, whereas during recovery phase it is mainly driven by internal processes, i.e., loading-unloading. Best fit is obtained when averaging the measured quantities over a few minutes, which means adjusting the spatial resolution of the measurements to the resolution of the model. Different time delays between the interplanetary magnetic field observations and those of Viking were examined. Best agreement was obtained, not surprisingly, for time delays corresponding to the estimated information transit time from the solar wind spacecraft to the ionosphere. In the geospace environment modeling (GEM) program, two models are considered for synthesis of sparse high-latitude data [Lotko, 1993]. Both models allow the computation of nearly instantaneous snapshots of electric field and potential distribution in the entire auroral region. The assimilative mapping of ionospheric electrodynamics (AMIE) model is used for calculation of high-latitude electric fields and currents from sets of localized observational data [Richmond and Kamide, 1988; Richmor•d et al., 1988; Richmor•d, 1992]. A similar model has also been used by Marklund et al. [1988]. See also Marklund arid Blomberg [1991] and Blomberg arid Marklur•d [1993]. The Inetitute of Terrestrial Mag-Copyright 1996 t)y the American Geophysical Union. Paper number 96JA00514. 0148-0227 / 96 / 96 J A-00514509.00 netism Electrodynamical Model (IZMEM)is another model for calculating the same parameters, but the input data are the interplanetary magnetic field (IMF) magnitude and direction [Levitir• et al., 1984; Feldsteir• arid Levitire, 1986; Papitashvili et al., 1994]. The influence of the IMF on the upper atmosphere electrodynamics is crucial also in the models of Friis-Christer•ser• et al. [1985] and Mishir• [1990]. The latter two models are used by their respective authors only, whereas the IZMEM model is publicly available through the World Data Center A for Rockets and Satellites [Bilitza, 1990]. The IZMEM model is here used to determine the global convection pattern and its temporal evolution during a number of passes of the Swedish satellite Viking over the northern high-latitude region. The model electric field is compared to the satellite observations along the trajectory, and the global convection pattern and its temporal evolution is estimated in the entire highlatitude region. The sensitivity to averaging of the correlation between the modeled and measured values is discussed. The averaging interval selected influences the sensitivity of the correlation to changes in the model, and it is of interest to determine to what extent the correlation coefficient is dependent on the correct timing of the changes between gross features of the convection system during the period studied. 19,921 19,922 FELDSTEIN ET AL.: HIGH-LATITUDE IONOSPHERE There is today a consensus that there are two processes responsible for the solar wind energy input to the magnetosphere during sUbstorms. These are direct driving and loading-unloading processes. Some fraction of the energy input is directly dissipated in the ionosphere by Joule heating and particle precipitation related to enhanced convection and enhanced ionospheric currents. This power dissipation is directly correlated with the solar wind parameters and is thus a driven process [Akasofu, 1981]. The remaining part of the power transfeted into the magnetosphere is stored temporarily in the Earth's magnetosphere and subsequently released at substorm breakup. The latter is known as loading-unloading process [Baker et al., 1984, 1993]. The delay time between a change in the IMF and the related effects in the ionosphere is different for the two processes. For the directly driven process it is 10-20 min due to the inductance of the magnetosphereionosphere system. For the loading-unloading process it is typically 40-60 min. Which one of these .processes dominates remains an open question.
Journal of Geophysical Research, 2005
During magnetic storms the ionospheric total electron content (TEC) at low-and midlatitudes often shows great enhancements, which may be associated with mechanisms producing midlatitude storm-enhanced density (SED). The TEC enhancements may result from different ionospheric drivers such as electric fields, neutral winds, and neutral composition effects. To study the importance of the ionospheric drivers in producing the TEC enhancement, we perform numerical simulations for the 29-30 October 2003 superstorm period in the American longitude sector ($ À70°W) using the Sheffield University Plasmasphere Ionosphere Model (SUPIM) with values for the neutral wind, temperature, and composition provided by the National Center for Atmospheric Research (NCAR) Thermosphere Ionosphere General Circulation Model (TIEGCM). Various numerical experiments were run to identify the relative importance of the storm-time ionospheric drivers. For carrying out the storm-time SUPIM simulation, the storm-time upward/poleward E Â B drifts are derived from ROCSAT-1 satellite measurements at low and equatorial latitudes and input to SUPIM, while the storm-time neutral wind and composition disturbances are obtained from TIEGCM run. The simulation results presented in this paper, mainly during the evening period, show that the enhanced upward E Â B drifts due to storm-time eastward penetration electric field can expand the low-latitude equatorial ionization anomaly (EIA) to higher latitudes and produce the TEC enhancement. However, by the effect of penetration electric fields alone, the TEC enhancement is less than by combining the storm-generated equatorward neutral winds and the penetration electric fields. Disturbance neutral composition effects decrease the plasma density at higher latitudes and increase it at low and equatorial latitudes. However, the composition effects do not produce a density increase as large as that produced by the neutral-wind and electric-field effects. Our simulations suggest that the storm-generated equatorward neutral winds play an important role in producing the TEC enhancement at low-and midlatitudes, in addition to the eastward penetration electric field.
Frontiers in Astronomy and Space Sciences, 2021
The solar wind has been seen as the major source of hot magnetospheric plasma since the early 1960’s. More recent theoretical and observational studies have shown that the cold (few eV) polar wind and warmer polar cusp plasma that flow continuously upward from the ionosphere can be a very significant source of ions in the magnetosphere and can become accelerated to the energies characteristic of the plasma sheet, ring current, and warm plasma cloak. Previous studies have also shown the presence of solar wind ions in these magnetospheric regions. These studies are based principally on proxy measurements of the ratios of He++/H+ and the high charge states of O+/H+. The resultant admixture of ionospheric ions and solar wind ions that results has been difficult to quantify, since the dominant H+ ions originating in the ionosphere and solar wind are indistinguishable. The ionospheric ions are already inside the magnetosphere and are filling it from the inside out with direct access from the ionosphere to the center of the magnetotail. The solar wind ions on the other hand must gain access through the outer boundaries of the magnetosphere, filling the magnetosphere from the outside in. These solar wind particles must then diffuse or drift from the flanks of the magnetosphere to the near-midnight reconnection region of the tail which takes more time to reach (hours) than the continuously large outflowing ionospheric polar wind (10’s of min). In this paper we examine the magnetospheric filling using the trajectories of the different ion sources to unravel the intermixing process rather than trying to interpret only the proxy ratios. We compare the timing of the access of the ionospheric and solar wind sources and we use new merged ionosphere-magnetosphere multi-fluid MHD modeling to separate and compare the ionospheric and solar wind H+ source strengths. The rapid access of the initially cold polar wind and warm polar cusp ions flowing down-tail in the lobes into the mid-plane of the magnetotail, suggests that, coupled with a southward turning of the IMF Bz, these ions can play a key triggering role in the onset of substorms and subsequent large storms.
Real-Time Dynamic Ionospheric Storm Modelling
esa-effect.net
As radio communications systems become more technologically advanced, there is increasing demand to predict terrestrial plasma environment during severe space weather events. One important element of terrestrial plasma prediction is the onset of the ionospheric storms and their development during the first 24-hour. In the paper we discuss why a dynamic ionospheric storm forecast model, currently under developed, is needed and how it may be used to meet current and future radio communications as well as space weather operational requirements. At this stage, the model provides foF2 critical frequency of the F2 layer values during severe storm from disperse ionospheric and satellite observations. It makes use of the real-time ACE observations of the solar wind parameters to identify the storm onset and its intensity. Then the corrected model parameters are calculated at single stations and predictive accuracy is assessed. This work is expected to result in a real-time dynamic ionospheric storm model that has potential as part of an ionospheric/plasmaspheric specification and forecasting system within the COST271 Action and European space weather initiatives.
Journal of Geophysical Research, 2008
1] We have investigated the thermospheric and ionospheric response to the 14-15 December 2006 geomagnetic storm using a Coupled Magnetosphere Ionosphere Thermosphere (CMIT) 2.0 model simulation. In this paper we focus on observations and simulations during the initial phase of the storm (about 8 h), when the shock was driving changes in geospace. The global ionospheric maps of total electron content (TEC), ionosonde data at four stations and Millstone Hill incoherent scatter radar (ISR) observations are compared with the corresponding simulation results from the CMIT model. The observations showed significant positive storm effects occurred in the Atlantic sector after the onset of this storm. The CMIT model is able to capture the temporal and spatial variations of the ionospheric storm effects seen in the GPS TEC observations, although the model slightly underestimates the daytime positive ionospheric storm in the South American sector. The simulations are also in agreement with the ionosonde and ISR ionospheric measurements. Term analysis of the ion continuity equation demonstrates that changes in the electric fields play a dominant role in generating the observed ionospheric positive storm effect in the American sector during the initial phase, although neutral winds and composition changes also contribute. The difference in the strength of the enhancements over North and South America can be explained by the slope of the topside electron density profiles in the two hemispheres. In the southern hemisphere electron densities decrease slowly with altitude, whereas the decrease is much more rapid in the northern (winter) hemisphere. The electric fields, therefore, cannot cause large increases in electron density by uplifting the plasma, so positive storm effects are small in the southern hemisphere compared with the northern hemisphere, even though the increase in h m F 2 is greater in the southern hemisphere. Nighttime changes in electron density in other longitude sectors are small, because the topside electron densities also decrease slowly with altitude at night.
Observed and modeled thermosphere and ionosphere response to superstorms
2007
1] Observations and numerical simulations of the response of the thermosphere and ionosphere to ''superstorms'' illustrate that multiple processes are operating. The initial response at high latitude is thermospheric heating, thermal expansion, high-velocity winds, wave surges, the initiation of a new global circulation, and the start of neutral composition changes. At low latitude, the initial response is driven by the penetration of magnetospheric electric fields, moving the equatorial ionization anomaly poleward, and enhancing both F region plasma densities and the total electron content at midlatitudes and low latitudes. Electron content also increases dramatically at the higher altitudes. In the later stages of the response, plasma densities begin to respond to the changing circulation; the transport of composition changes to midlatitudes and low latitudes; and the generation of disturbance dynamo effects, which either compete or combine with penetration fields. The observations and modeling indicate that all the processes have a significant impact at some time and place during the storm. Citation: Fuller-Rowell, T., M. Codrescu, N. Maruyama, M. Fredrizzi, E. Araujo-Pradere, S. Sazykin, and G. Bust (2007), Observed and modeled thermosphere and ionosphere response to superstorms, Radio Sci., 42, RS4S90,
Advances in Space Research, 2006
The global numerical upper atmosphere model (UAM) has been used to investigate the effects of the April 2002 magnetic storms on the EarthÕs ionosphere and thermosphere. Results of UAM simulations have been compared with experimental plasma density and temperatures obtained by seven incoherent scatter radars and with neutral composition and temperature data provided by the NRLMSISE-00 model. The UAM calculations of plasma density and temperatures were performed using three versions of neutral constituents: (1) the NRLMSISE-00 neutral composition and temperature; (2) fully self-consistently determined theoretical neutral composition and temperature obtained using NRLMSISE-00 as an initial condition; (3) the same as in (2) but with simulations starting from the steady state theoretical thermosphere solution as an initial condition on April 15, 2002. The model calculations with the ''theoretical thermosphere'' give a larger thermospheric response to the magnetic storm (neutral temperature increase and O/N2 ratio decrease) and a more distinct negative ionospheric storm effect than the calculations with the NRLMSISE, resulting in N e , T i and T e calculations closer to the radar observations. In most cases, when the model used the MSIS-specified neutral atmosphere, it performed the worst, indicating that an interactive thermosphere is needed to model the ionosphere accurately.
Annales Geophysicae, 2000
Current theories of F-layer storms are discussed using numerical simulations with the Upper Atmosphere Model, a global self-consistent, time dependent numerical model of the thermosphere±iono-sphere±plasmasphere±magnetosphere system including electrodynamical coupling eects. A case study of a moderate geomagnetic storm at low solar activity during the northern winter solstice exempli®es the complex storm phenomena. The study focuses on positive ionospheric storm eects in relation to thermospheric disturbances in general and thermospheric composition changes in particular. It investigates the dynamical eects of both neutral meridional winds and electric ®elds caused by the disturbance dynamo eect. The penetration of short-time electric ®elds of magnetospheric origin during storm intensi®cation phases is shown for the ®rst time in this model study. Comparisons of the calculated thermospheric composition changes with satellite observations of AE-C and ESRO-4 during storm time show a good agreement. The empirical MSISE90 model, however, is less consistent with the simulations. It does not show the equatorward propagation of the disturbances and predicts that they have a gentler latitudinal gradient. Both theoretical and experimental data reveal that although the ratio of [O]/[N 2 ] at high latitudes decreases significantly during the magnetic storm compared with the quiet time level, at mid to low latitudes it does not increase (at ®xed altitudes) above the quiet reference level. Meanwhile, the ionospheric storm is positive there. We conclude that the positive phase of the ionospheric storm is mainly due to uplifting of ionospheric F 2 -region plasma at mid latitudes and its equatorward movement at low latitudes along geomagnetic ®eld lines caused by large-scale neutral wind circulation and the passage of travelling atmospheric disturbances (TADs). The calculated zonal electric ®eld disturbances also help to create the positive ionospheric disturbances both at middle and low latitudes. Minor contributions arise from the general density enhancement of all constituents during geomagnetic storms, which favours ion production processes above ion losses at ®xed height under daylight conditions.
Thermospheric wind during a storm-time large-scale traveling ionospheric disturbance
Journal of Geophysical Research, 2003
A prominent large-scale traveling ionospheric disturbance (LSTID) was observed in Japan during the major magnetic storm (Dst $ À358 nT) of 31 March 2001. It was detected as enhancements of the 630-nm airglow and foF2, GPS-TEC variations, and a decrease in F-layer virtual height at 1700-1900 UT (0200-0400 LT). It moved equatorward with a speed of 600m/s.ThedecreaseintheF−layerheightwasalsodetectedbytheMUradaratShigaraki.ThermosphericwindvariationswereobservedbytheMUradarthroughiondriftmeasurementandbyaFabry−Perotinterferometer(FPI)throughaDopplershiftofthe630−nmairglowlineatShigaraki.ThewinddatashowaturnofthemeridionalwindfromAˋ94m/s(equatorward)to+44m/s(poleward)duringtheLSTID,indicatingthatanintensepolewardwindinthethermospherepassedoverShigarakiasanatmosphericgravitywaveandcausedtheobservedionosphericfeaturesoftheLSTID.Intensepolewardwindwasalsodetectedatmesosphericaltitudes(95−100km)bytheMUradar(throughmeteorechoes)andbytheFPI(throughthe558−nmairglow)withadelayof600 m/s. The decrease in the F-layer height was also detected by the MU radar at Shigaraki. Thermospheric wind variations were observed by the MU radar through ion drift measurement and by a Fabry-Perot interferometer (FPI) through a Doppler shift of the 630-nm airglow line at Shigaraki. The wind data show a turn of the meridional wind from À94 m/s (equatorward) to +44 m/s (poleward) during the LSTID, indicating that an intense poleward wind in the thermosphere passed over Shigaraki as an atmospheric gravity wave and caused the observed ionospheric features of the LSTID. Intense poleward wind was also detected at mesospheric altitudes (95-100 km) by the MU radar (through meteor echoes) and by the FPI (through the 558-nm airglow) with a delay of 600m/s.ThedecreaseintheF−layerheightwasalsodetectedbytheMUradaratShigaraki.ThermosphericwindvariationswereobservedbytheMUradarthroughiondriftmeasurementandbyaFabry−Perotinterferometer(FPI)throughaDopplershiftofthe630−nmairglowlineatShigaraki.ThewinddatashowaturnofthemeridionalwindfromAˋ94m/s(equatorward)to+44m/s(poleward)duringtheLSTID,indicatingthatanintensepolewardwindinthethermospherepassedoverShigarakiasanatmosphericgravitywaveandcausedtheobservedionosphericfeaturesoftheLSTID.Intensepolewardwindwasalsodetectedatmesosphericaltitudes(95−100km)bytheMUradar(throughmeteorechoes)andbytheFPI(throughthe558−nmairglow)withadelayof2 hours from the thermospheric wind, indicating downward phase progression of the wave. Generation of the observed poleward wind in the auroral zone was investigated using magnetic field data and auroral energy input estimated by the assimilative mapping of ionospheric electrodynamics (AMIE) technique. We suggest that simple atmospheric heating and/or the Lorentz force in the auroral zone do not explain the observed poleward wind enhancement.